1. Field of the Invention
The present invention relates to a data protective microprocessor circuit according to the preamble of claim 1.
Microprocessor circuits of the stated type are used chiefly in so-called chip cards, i.e. identity cards, credit cards, posting cards and the like, which are equipped with integrated circuits. However, the microprocessor circuits can also be used in so-called payment modules which communicate with the abovementioned cards via suitable interfaces.
2. Description of the Prior Art
To facilitate the understanding of the invention, the following description will relate to the application of the microprocessor circuit in cards.
A card with a microprocessor was described for the first time in DE-OS 27 38 113. One of the essential advantages of such a card is the versatile possibilities of use by the card owner. The microprocessor contained in the integrated circuit or the card and the corresponding storage means permit extensive data processing in the card itself, whereas cards provided with a magnetic strip, for example, make it necessary to perform all data processing operations externally.
The card manufacturer can equip the microprocessor with a resident operating system which performs fundamental functions, for example procedures for comparing an externally inputted code with a stored code and the like. The memories belonging to the microprocessor serve not only to store the operating system but also to store certain applications and parameters which are necessary e.g. for security checking and must be kept absolutely secret.
A versatile application of the cards is obtained if one starts out from an operating system with associated programs, defines certain interfaces and reserves a memory or memory area for a so-called secondary program. The card manufacturer provides for the user, i.e. the card-issuing organization, a memory or memory area for programming its secondary program. The organization can fix specific operations in this secondary program which are independent of the operating system and relate only to the particular organization.
A further conceivable variant is for not only one organization to program its secondary program into the prefabricated chip card but for several different organizations to store their corresponding programs.
In any case one must make sure that security-relevant data which are part of the operating system or the individual secondary programs are protected from unauthorized access.